Fats and oils (hereinafter referred to sometimes as fats/oils) contain esters called triglycerides as the main raw material, and alkyl fatty esters are produced from fats and oils by ester exchange with alcohols. Particularly, alkyl fatty esters produced from vegetable oils are regarded as important biodiesel fuel oil not increasing carbon dioxide, from the viewpoint of countermeasures against global warming. High-quality standards are established for alkyl fatty esters as biodiesel fuel oil, and in Europe, the acid value of alkyl fatty esters is established to be not higher than 0.5 mg KOH/g. That is, it is required to produce high-quality alkyl fatty esters. It is further desired to use alkyl fatty esters of low acid value in production of fatty alcohols from alkyl fatty esters.
As processes for producing alkyl fatty esters from fats/oils and alcohols, various processes are known. In this reaction, for example, JP-A 2004-27170 describes that raw materials are reacted in the presence of an alkali catalyst after removal of water from raw oils by a water-absorbing filter. With respect to an acid catalyst, JP-A 2003-246997 makes use of sulfuric acid, hydrochloric acid etc.
On one hand, JP-A56-65097 describes a multistage process wherein prior to reaction, glycerin is separated and then crude esters are fed to a next stage. In JP-A 61-254255, alcohols are first evaporated from a reaction mixture and then unreacted materials are refluxed while glycerin is removed by phase separation.